Method of making alkali-soluble alumina.



PAUL R. HERSHMAN, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE MINERAL ?BODUCT$ GOMPANY, OF NEW YORK, N. Y., A. CORPUBATION: OF WEST VXBGIHIA.

ME'IHQD SF MAKING ALKALI-SOLUBLE ALUMINA.

Zuo Drawing.

ment of calcined alunite, alum rock, alum stone and the like, for the purpose of converting the alumina into a condition which renders it soluble in alkali.

The present invention is based upon the discovery that by heating palcined alunite to a suitable temperature in admixture with carbon, (for instance, powdered coal, POW? dered coke, lamp black, or the like,) the calcined alunite Will be converted into a condition in which it will be partly or Wholly soluble in alkali. For instance, the

, alumina, mixed with 20% to 50% of carbon,

and treated in a current of a gas which will not consume the carbon, (as, for instance, nitrogen, or carbon monoxid) or which will not materially consume the carbon (as, for instance, producer gas) begins to become soluble at about 14.50". C. At about 1550 0., say 50% of the alumina becomes soluble, and at about.1650 C. the solubility is substantially complete. Conducting the operation in a current of air or in a current of carbon dioxid gives lower results, particularly if no precautions are taken to compensate for any accompanying consumption of the'carbon in the charge, Accordingly, where any such carbon-consuming gas is employed the charge should contain a sutllci'ent excess of carbon to compensate for that which is consumed.

The heating operation is to be maintained for a period ranging from l} to 2 hours ac cording to the quantity treated and the available facilities for bringing the entire mass to the desired maximum. degree of heat. The termination of the operation may be established, for instance, by taking test samples from the charge until a test sample is obtained which will dissolve in :boiling alkali. "it is found that heating the mixture of alumina vand carbon at the high Application filed October 29, 191%.

Specification of Letters Patent. Patqgmtggfl App, 1915,

Serial Ho. 889,203.

range of temperature indicated usually re sults in the conversion of some portion of the alumina into aluminum carbid, and that with further increase of temperature the relative proportion of 'carbid to maid increases. Not only the alumina, but also the aluminum carbid produced, are found to enter into solution in heated or boiling alkali. Accordingly, the product containing the alkali-soluble aluminum. oXid and the aluminum carbids is dissolved by heating the product (preferably to the boiling point) in a solution of sodium hyclroxid, in the proportion of 1-7,- to 2 parts by weight of actual sodium hydroxid to one part by weight of aluminum oxid, or one part by Weight of aluminum carbid, calculated to the 'oxid. The heating operation is facilitated by pressure. The alumina may then be recovered from the solution in a pure state by the well-known Bayer process or any other suitable process adapted for the purpose as will be Well understood by those skilled in the art.

While the practice of the invention is not restricted to the use of any particular'apparatus, it will be found-convenient to conduct the operation in the usual inclined rotatory kiln. 7

it will be understood that before subjecting the calcined alunite to the treatment herein proposed, it will be desirable to re cover from it the potash salts, either by leaching as described in U. S. Patent issued to Howard F.-Chappell, No.1,070,324, under date of August 12, 1913, or by volatilization as described in a pending application of Charles H. MacDoWelh Serial No. 854,278, filed July 3, 1914. It is not commercially feasible, however, to absolutely remove the alkali salts in their entirety from the cal calcined alunite apparently tends toimprove the leiiiciency of the operation, inasmuch as calcined alunite 1s very readily rendered soluble by the treatment proposed. 3 may say, however, that in so .lar asl am aware, the process descr bes. 1S new in its applicasoluble in alkali, mainly as duced and I therefore desire that-the inven f tion should have a correspondingly 'comp're-i hensive interpretation.

What I,claim is:

1. The method of treating alumina, which consists in heating it in admixture with carbon up to a temperature sufficient to leave it soluble in alkali mainly as oxid.

2. The method of treating alumina, which consists in heating it, in admixture with carbon, and in the presence of a protective gas, up to a temperature sufficlent to leave it 3. The method'of treating alumina,lwhich consists in heating it, in admixture with car:

bon, and in the presence of a lion-nitrifying atmosphere, to a temperature suflicient to make it soluble in alkali. i

4. The method of treating aluniteand the like, which consists in calcining i iaand there-'" uble in alkali mainly as oxid.

5. Themethod of treating alunite, Which (after heating it, in admixture with carbon up to a temperature sufficient to leave it solconsists in calcining it, and thereafter heating it, in admixture with carbon, and in the presence of a protective gas, up to a temperature sufli'cient to leave it soluble in elkali, mainly as oxid.

6. The method of treating alunite, which consists in calcining it, and thereafter heating it, in admixture with carbon, and in the presence of a' non-nitrifying atmosphere, to a temperature suflicient to make it soluble in alkali.

Intestimony whereofI aifix in presence of two-witnesses.

, PAUL R. HERSHMAN:

Witnesses:

my signature, 

